Method and system for adaptive guard interval (gi) combining

ABSTRACT

A method and system for combining a guard interval and a corresponding portion of a received symbol, whereby when receiving a signal that contains the symbol with a guard interval corresponding to the symbol, a portion of the guard interval that is free from inter-symbol interference may be extracted, and the extracted portion of the guard interval may be combined with the corresponding portion of the symbol. The extracting and combining may be done after a determining, based on a delay profile provided by the received signal, that a delay spread is smaller than a predetermined channel delay. The delay spread may be determined by filtering an instantaneous delay spread associated with the received signal. The filtering may be performed using a 1-tap infinite impulse response low-pass filter. The low-pass filter may include a time constant that is the inverse of a maximum Doppler frequency shift.

CLAIM OF PRIORITY

This patent application makes reference to, claims priority to andclaims benefit from U.S. Provisional Application Ser. No. 61/433,933which was filed on Jan. 18, 2011.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

[Not Applicable].

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[Not Applicable].

MICROFICHE/COPYRIGHT REFERENCE

[Not Applicable].

FIELD OF THE INVENTION

Certain embodiments of the invention relate to communications. Morespecifically, certain embodiments of the invention relate to a methodand system for adaptive guard interval (GI) combining.

BACKGROUND OF THE INVENTION

Communication devices may be operable to communicate using wirelessand/or wired connections, and be utilized to receive inputs, store andprocess data, and provide outputs for various applications running on orvia these devices. Communication devices may comprise, for example,personal computers (PCs), laptops or notebook computers, servers,cellular and smart phones or other similar handheld mobile devices,wireless access points, or other like devices. A communication devicemay comprise dedicated internal or external components for enablingnetwork access operations, to enable sending and/or receiving data, inthe form of packets, via wired and/or wireless connections, configuredand/or structured in accordance with supported interfaces and/orprotocols. Communication via the wireless and/or wired connectionscomprises embedding data into radio frequency (RF) signals. In thisregard, the communication devices may be operable to transmit and/orreceive RF signals carrying exchanged data, with the RF signals beingconfigured in accordance with corresponding wired and/or wirelessprotocols or standards. Configuring the RF signals during wirelessand/or wired communications may comprise use of particular modulationschemes, in accordance with the corresponding communication protocol orstandard.

In this regard, RF modulation comprises modifying and/or configuring oneor more signal characteristics based on the data carried therein. Forexample, with analog communications (e.g., traditional radio or TVbroadcast), RF modulation schemes may comprise amplitude modulation (AM)based schemes, frequency modulation (FM) based schemes, and/or phasemodulation (PM) based schemes. With digital communication, RF modulationmay also incorporate and/or be based on “keying”—where the carriersignals are modulated to take one of limited number (typically two,corresponding to logic ‘0’ and ‘1’) values at all times. In this regard,exemplary digital modulation schemes may comprise phase-shift keying(PSK) based schemes, frequency-shift keying (FSK) based schemes,amplitude-shift keying (PSK) based schemes, and quadrature amplitudemodulation (QAM) based schemes.

Therefore, facilitating proper reception of the information, at thereceiver side, requires knowledge of the utilized modulation scheme,such that the corresponding demodulation processing may be performed toenable extracting the carried data. In addition, the receptionprocessing may also incorporate particular aspects to account for andaddress any unintended changes to the RF signals during thecommunication. For example, during wireless communications RF signalsmay be changed due to movement to one or more of the communicationdevices, to reflection off or travelling through physical objects in thepath, and/or due to external interference and/or electronic noise in thereceiver device.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

A system and/or method is provided for adaptive guard interval (GI)combining, substantially as shown in and/or described in connection withat least one of the figures, as set forth more completely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an exemplary communication setup,which may be utilized in accordance with an embodiment of the invention.

FIG. 2 is a block diagram illustrating an exemplary use of guardinterval (GI) combining, in accordance with an embodiment of theinvention.

FIG. 3A is a block diagram illustrating an exemplary communicationdevice that support guard interval (GI) combining, in accordance with anembodiment of the invention.

FIG. 3B is a block diagram illustrating an exemplary signal processingmodule that support guard interval (GI) combining, in accordance with anembodiment of the invention.

FIG. 4 is a flow chart that illustrates exemplary steps for adaptiveguard interval (GI) combining, in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor adaptive guard interval (GI) combining. In various embodiments ofthe invention, adaptive guard interval (GI) combining may be performedby a communication device during reception of RF signals, on a receivedsignal that comprises one or more symbols preceded by correspondingguard interval(s) and the symbol. In this regard, during GI combining,the guard interval(s) or portion(s) thereof may be combined withcorresponding portion(s) of received symbol(s), to enable reducing thenoise level in a channel and to reduce both the noise level andinter-carrier interference (ICI) for channels having short or mediumdelay spread. The adaptive GI combining may comprise determining, basedon an impulse response provided by the received signal and relating to achannel used in communication thereof for example, whether a delayspread is smaller than a predetermined threshold for channel delay. Thisthreshold is a design parameter determined by the maximum delay spreadto be accommodated by the adaptive GI combining. In the event that thedelay spread is determined to be smaller than the predeterminedthreshold, a portion of the guard interval that is free frominter-symbol interference (ISI) may be extracted, and the extractedportion of the guard interval may be combined with the correspondingportion of the received symbol. The delay spread may be determined byfiltering an instantaneous delay spread which is associated with thereceived signal. The filtering may be performed by means of a 1-tapinfinite impulse response low-pass filter. In this regard, the low-passfilter includes a time constant which equals the inverse of a maximumDoppler frequency shift.

FIG. 1 is a block diagram illustrating an exemplary communication setup,which may be utilized in accordance with an embodiment of the invention.Referring to FIG. 1, there are shown communication devices 100 _(A) and100 _(B), which may communicate via connection 110.

Each of the communication devices 100 _(A) and 100 _(B) may comprisesuitable logic, circuitry, interfaces, and/or code for enablingcommunication over wired and/or wireless connections. In this regard,the communication devices 100 may support a plurality of wired and/orwireless interfaces and/or protocols, and may be operable to performnecessary processing operations to facilitate transmission and/orreception of signals (e.g. RF signals) over supported wired and/orwireless interfaces. Exemplary communication devices may comprisecellular and smart phones or similar handheld devices, tablets, personalcomputers, laptops or notebook computers, servers, personal mediaplayers, personal digital assistants, set top boxes, wireless accesspoints and/or cellular base stations, and/or other like devices.Exemplary wireless protocols or standards, which may be supported and/orused by the communication devices 100 _(A) and 100 _(B) forcommunication therebetween, may comprise wireless personal area network(WPAN) protocols, such as Bluetooth (IEEE 802.15) and ZigBee; wirelesslocal area network (WLAN) protocols, such as WiFi (IEEE 802.11);cellular standards, such as GSM/GPRS/EDGE, UMTS, HSDPA, CDMA2000; 4Gstandards, such as WiMAX (IEEE 802.16) and LTE; Ultra-Wideband (UWB);Extremely High Frequency (EHF—e.g. 60 GHz); and/or Digital TV Standards,such as DVB-T/DVB-H, and ISDB-T. Exemplary wired protocols and/orinterfaces may comprise Ethernet (IEEE 802.3), Digital Subscriber Line(DSL), Integrated Services Digital Network (ISDN), and/or FiberDistributed Data Interface (FDDI); or wireless standards, such as WLAN(IEEE 802.11).

In operation, the communication devices 100 _(A) and 100 _(B) maycommunicate over the connection 110. In this regard, communication overthe connection 110 may comprise transmission and reception of RF signalswhich are utilized to carry data exchanged between the communicationdevices 100 _(A) and 100 _(B). The RF signals communicated over theconnection 110 may be configured in accordance with corresponding awired and/or wireless protocol or standard. In this regard, configuringthe RF signals may comprise use of particular modulation schemes, inaccordance with the corresponding communication protocol or standard.One of the modulation schemes that has recently been widely deployed andused is Orthogonal Frequency-Division Multiplexing (OFDM), wherebydigital data may be encoded on multiple sub-carrier frequencies, witheach sub-carrier being modulated with a conventional modulation scheme,such as quadrature amplitude modulation (QAM) or phase-shift keying(PSK) at a low symbol rate, thus enabling maintaining total data ratessimilar to conventional single-carrier modulation schemes in the samebandwidth. The OFDM scheme provides an efficient use of radio spectrumby placing modulated subcarriers as close as possible without causinginter-carrier interference (ICI). Exemplary communication wired andwireless standards that incorporate use of OFDM comprise power linecommunication (PLC), Asymmetric digital subscriber line (ADSL), digitalaudio broadcast (DAB), digital video broadcast (DVB/ISDB-T), wirelessLAN (IEEE 802.11a/g/n), and WiMAX (IEEE 802.16).

Accordingly, during communication between the communication devices 100_(A) and 100 _(B), the transmitter device applies the proper modulationscheme (as dictated by the utilized communication standard) totransmitted RF signals during encoding of data carried thereby, and thereceiver device applies the proper, corresponding demodulationprocessing, as dictated by the utilized modulation scheme, to enableextracting the carried data. Furthermore, the receiver device may applyadditional functions and/or processing to ensure that the data carriedby the RF signals is extracted correctly. In this regard, the additionalprocessing may be tailored to account for the propagation of the RFsignals, and to addressing potential issues related thereto. Forexample, during wireless communications between devices 100 _(A) and 100_(B), RF signals and the reception thereof may be affected or altered bymovement of one or both of the devices, by RF signals reflecting off ortravelling through physical objects, and/or due to external interferenceand/or electronic noise in the receiver device. In this regard, duringwireless communication the path between the transmitter and the receiver(e.g., devices 100 _(A) and 100 _(B)) may vary from simple line-of-sightto one that is severely obstructed by buildings and mountains.Therefore, the received signal in a multipath environment may contain aseries of attenuated, time-delayed, phase shifted replicas of thetransmitted signal. In wired and/or wireless communications, themultipath environment is usually characterized by channel impulseresponse, where the difference between the time of arrival of theearliest significant multipath component and the time of arrival of thelatest multipath component is commonly referred as delay spread ormaximum delay spread. Furthermore, the moving speed of a mobilereceiver, for example, may impact the signal fading level. In thisregard, fading may be caused by interference between two or moreversions of the transmitted signal which arrive at the receiver atdifferent times due to multipath.

Due to the relative motion between the receiver and the transmitter(e.g., between a moving cellular phone and stationary base station),each multipath wave may experience a frequency shift. The frequencyshift in received signal frequency due to motion is called the Dopplerfrequency shift and is directly proportional to the velocity anddirection of motion of the device(s) with respect to the direction ofarrival of the received multipath wave. The Doppler frequency shift canbe calculated as:

$\begin{matrix}{{fD} = {V*\frac{f}{c}*{\cos (\varphi)}}} & (1)\end{matrix}$

where v is the receiver velocity; f is the carrier frequency of thetransmitted signal; c is the speed of light; φ is the angle between themotion direction (e.g., of the receiver device) and the incoming signaldirection; and fD is the Doppler frequency shift.

In an aspect of the invention, the reception of RF signals andextraction of data carried therein may be enhanced, and/or some of theissues arising from and/or relating to the propagation of the RF signalsmay be remedied and/or mitigated, by taking advantage of certaincharacteristics or attributes of the modulation scheme used by thecommunication devices. For example, in OFDM, since the received signalin a multipath channel may contain a series of attenuated, time-delayed,phase shifted replicas of the transmitted signal, the generation of thetransmitted signals may comprise attaching guard intervals totransmitted symbols, wherein the guard interval may be correspond to atime period greater than the maximum delay spread of the channel toprevent inter-symbol interference (ISI) due to delay spread.

A simplified baseband model for OFDM transmission and reception is shownin FIG. 1. At the transmitter side 120, transmitting OFDM modulated RFsignals may comprise converting modulated, data-bearing sub-carriers (infrequency domain) X_(k) through Inverse-Fast-Fourier-Transform (IFFT)122 to time-domain signal x_(n), after a parallel-to-serial (P/S)conversion 124. A guard interval (GI) addition 126 is then performedwhereby a guard interval (GI) 132 may be added to the beginning of eachOFDM symbol 128 to handle the frequency selective fading—that is forpreventing inter-symbol interference (ISI) due to delay spread. Theguard interval (GI) 132 may be generated by replicating a particularportion (e.g. portion 130) of the OFDM symbol 128, which may comprise alast portion of the OFDM symbol 128—also commonly referred to as cyclicprefix (CP). The OFDM modulated RF signal is then communicated over thechannel 150.

At the receiver side 140, the RF signal is received from the channel150, and the sub-carriers are obtained via serial-to-parallel (S/P)conversion 142, and then a guard interval (GI) removal 142 is applied toremove the guard intervals 132. Then, a Fast-Fourier-Transform (FET) 146may be performed to convert the time-domain discrete samples y_(n) intocorresponding frequency-domain modulated sub-carriers Y_(m), from whichcarried data is obtained (e.g., subsequent to demodulation).

The channel 150 may be modeled as having both frequency-selective fadingand time-selective fading, where frequency-selectivity is characterizedby delay spread and time-selectivity is characterized by Dopplerfrequency shift. Although OFDM is known to be robust againstfrequency-selective fading as the multi-carrier scheme can turnfrequency-selective channel into a bank of frequency-flat channels, itis vulnerable to Doppler shift. In this regard, the received signal, atthe receiver side 140, is convolution of transmitted signal and thechannel 150. The implicit assumption of the FFT operation 146 performedat the receiver side 140 is that the channel 150 remains constant withinthe time interval of one OFDM symbol. The channel 150, however, may varyover time, even during the time interval of one OFDM symbol. Thetime-varying nature of the channel may be caused by, for example, therelative motion between the receiver and the transmitter devices, and/orby objects traversed or encountered along the signal path. Suchtime-variation may introduce inter-carrier-interference (ICI) that needto be mitigated in order to improve the reception performance.

In various embodiments of the invention, such time-variation relatederrors may be mitigated by taking advantage of the guard intervals,which are simply discarded in conventional systems. In other words, datacarried in the guard intervals 132, which correspond to portions of theOFDM symbols 128, may be utilized to compensate for interference causedby time-variations in the channel.

For example, assuming the time-varying discrete channel, h_(n), has onlyone tap to simplify the derivations, the received signal at time index ncan be modeled as:

$\begin{matrix}{y_{n} = {{{h_{n} \cdot x_{n}} + {noise}} = {{\frac{1}{N}{\sum\limits_{k = 0}^{N - 1}\; {X_{k} \cdot ^{{j2\pi}\frac{kn}{N}} \cdot h_{n}}}} + {noise}}}} & (2)\end{matrix}$

where X_(k) is modulated sub-carriers in frequency domain, x_(n) is thetransmitted time-domain signal, y_(n) is the received time-domainsamples after removing guard intervals, and noise represent the totalexternal interference and/or electronic noise at the receiver side.

To recover the modulated data sub-carriers, Y_(m), FFT operation 146 isperformed on the received time-domain samples y_(n) in accordance withthe model:

$\begin{matrix}{Y_{m} = {{\sum\limits_{n = 0}^{N - 1}\; {y_{n} \cdot ^{{- {j2\pi}}\frac{mn}{N}}}} = {{\sum\limits_{n = 0}^{N - 1}\; {\frac{1}{N}{\sum\limits_{k = 0}^{N - 1}\; {X_{k} \cdot ^{{j2\pi}\frac{kn}{N}} \cdot h_{n} \cdot ^{{- {j2\pi}}\frac{mn}{N}}}}}} + {noise}}}} & (3)\end{matrix}$

which may be rewritten as:

$\begin{matrix}{Y_{m} = {{\sum\limits_{k = 0}^{N - 1}\; {X_{k}\frac{1}{N}{\sum\limits_{n = 0}^{N - 1}\; {h_{n} \cdot ^{{j2\pi}\frac{{({k - m})}n}{N}}}}}} + {noise}}} & (4)\end{matrix}$

This can be simplified as:

$\begin{matrix}{Y_{m} = {{X_{m}\frac{1}{N}{\sum\limits_{n = 0}^{N - 1}\; h_{n}}} + {\sum\limits_{{k = 0},{k \neq m}}^{N - 1}\; {X_{k}\frac{1}{N}{\sum\limits_{n = 0}^{N - 1}\; {h_{n} \cdot ^{{j2\pi}\frac{{({k - m})}n}{N}}}}}} + {noise}}} & (5)\end{matrix}$

It is straightforward to show that, if h_(n) is constant over the OFDMsymbol time, i.e., h_(n)=h for n=0 . . . N−1, the second term in theabove equation will vanish, and Y_(m)=h·X_(m)+noise. However, as h_(n)changes over time, the second term appears as interference tosub-carrier m from the rest of modulated sub-carriers.

It can be shown that the faster the channel (e.g. channel 150) changes,the larger the interference becomes and the more severe the performanceis affected. Also, it can be seen that the power of theinter-carrier-interference (ICI) term is proportional to the signalpower. Accordingly, under the worst high Doppler and high transmissionpower scenario, the ICI term may dominate the performance sincesignal-to-interference-and-noise ratio (SINR) will not benefit fromincreasing the transmit power since the ICI power increasescorrespondingly as the transmit power increases. Therefore, this effectmust be properly mitigated to avoid error floors on the Bit-Error-Rate(BER) and Packet-Error-Rate (PER).

In OFDM based communications, the length of the guard interval (GI) maybe determined, e.g. by design, to be long enough to guarantee that nointer-symbol-interference (ISI) is experienced. However, for channelscharacterized by predictable noise model, such as additive whiteGaussian noise (AWGN), and having short delay spread, much of the guardinterval is free of ISI and contains the same data and channelinformation as the last portion of the OFDM symbol. The quality ofreception can be improved by using this redundant information. This maybe more beneficial for short delay spread but high Doppler environment,where the channel state information bearing in the guard interval canreduce the overall time-variation and reduce the ICI.

Accordingly, in various embodiments of the invention, communicationdevices (e.g. devices 100 _(A) and/or 100 _(B)) may adaptively combine,during reception of OFDM communication, a portion of the guard interval(GI) with a corresponding portion of the OFDM symbol, to reduce thenoise level in the channel and/or inter-channel interference (ICI) wherethe GI duration is longer than the channel delay spread. In embodimentof the invention, the receiving communication device may automaticallycombine a portion or an entire GI with a corresponding portion of theOFDM symbol based on estimated channel impulse response, and mayadaptively track the variation of the channel.

To maintain orthogonality, the receiving and transmitting devices needto remain perfectly synchronized. Accordingly, the receiving andtransmitting devices may have to use exactly the same modulationfrequency and the same time-scale for transmission. In some instances,one of the devices may be moving—e.g. the receiving device may be amoving cellular phone, whereas the transmitting device may be astationary base station—and the relative motion between the receivingand transmitting devices may cause a Doppler shift in frequency andvariation in the propagation delay, i.e., the difference of the time oftransmission and the time of arrival of the earliest significantmultipath component. Accordingly, in an embodiment of the invention, thereceiving device may adjust the timing for the FFT operation performedthereby during reception operations to account for that relativemovement and the resulting Doppler frequency shift. In this regard, theadjustment may be based on, for example, the delay spread between thereceiving and transmitting devices. The channel impulse response may betime-varying when a mobile or a moving receiving device moves across amultipath environment. For example, the channel may slowly or abruptlychange from short echo (short delay spread) to long echo (long delayspread), and back.

FIG. 2 is a block diagram illustrating an exemplary use of guardinterval (GI) combining, in accordance with an embodiment of theinvention. Referring to FIG. 2, there is shown an OFDM symbol 200,preceded by a guard interval (GI) 210, which may be received andproceeded by the a receiving communication device, such communicationdevice 100 _(A) or 100 _(B), during OFDM communication.

In operation, at least a portion of the GI 210 may be combined 220 withcorresponding portion of the OFDM symbol 200, which may enable reducingchannel noise and/or inter-channel interference (ICI). The GI 210 maycomprise an inter-symbol interference (ISI) effected portion 210 _(A)and an ISI-free portion 210 _(B). The delineation 240 between theISI-effected 210 _(A) and the ISI-free portion 210 _(B) may correspondto, for example, the last detected channel multipath component.Accordingly, during GI combining 220, the ISI-effected portion 210 _(A)of the GI 210 may be discarded, while the ISI-free portion 210 _(B) maybe extracted, and added to corresponding portion of the OFDM symbol 200.The sum may then be divided by 2 to insert back to the OFDM symbol. Inan embodiment of the invention, the GI combining may be performed byperforming the addition and then right-shifting the sum by 1 bit. GIcombining may enable benefiting from the ISI-free portion 210 _(B) ofthe GI 210, and may result in an OFDM symbol that may be more robustagainst Doppler Shift than a symbol obtained by completely and simplydiscarding the GI, as done in conventional systems.

In an embodiment of the invention, the receiving device may beconfigured to begin the FFT operation a few samples earlier than thereal start of the OFDM symbol 200—i.e., the FFT window may be shiftedrelative to the start of the OFDM symbol 200 by a particular margin 230.Such configuration of the FFT operation may enable obtaining a morerobust timing estimation. Accordingly, during GI combining 220 only partof the ISI-free portion 210 _(B) of GI 210 may be extracted and added tothe corresponding portion of the OFDM symbol, with the part 210 _(C) ofthe ISI-free portion 210 _(B) that correspond to the shifted start pointof FFT operation being excluded from the GI combining operation. Inother words, in such instances only the part of the GI 210 that is ISIfree and precedes the start of the FFT window is used during GIcombining.

The ISI-effected portion 210 _(A) of the GI 210 may be determined by thereceiving device during reception of the OFDM communication. Thisdetermination may be performed continuously and dynamically duringreception of OFDM based signals. The determination of the ISI-effectedportion 210 _(A) may be based on estimated channel impulse response,with the remaining portion of the GI being considered ISI-free portion210 _(B), and thus being (potentially) subject to GI combining ratherthan being wasted as the case in the conventional systems. Thedelineation 240 of the ISI-effected 210 _(A) may correspond to thedetected last channel multipath component.

In an embodiment of the invention, the receiving device (e.g. device 100_(B) of FIG. 1) may not extract the GI 210 when the receiving devicedoes not have accurate timing information of the start of the FFTwindow, as adding the GI 210 (or any portion thereof) to the OFDM symbol200 in this stage may not improve the signal to noise ratio of thesymbol.

In an embodiment of the invention, the receiving device may trackchanges in the delay spread associated with the reception channel afterthe start time of the FFT operation is determined. This may be necessarybecause the receiving device may not be able to accurately estimate thechannel each time. For example, the receiving device may falsely detecta long echo where there is none, and thus may waste a good portion ofthe GI 200. Furthermore, the channel impulse response may slowly changeover time as well. Therefore, in order to maximize the gain of the GIcombining, the receiving device may instantaneously estimate the maximumdelay spread. In other word, instead of estimating the maximum delayspread based on impulse response obtained from multiple OFDM symbols,the delay spread is estimated per OFDM symbol and filtered to obtain anaverage value. The filtering may be performed using a low-pass filter,which may enable averaging out impact of false maximum delay spreads.

FIG. 3A is a block diagram illustrating an exemplary communicationdevice that support guard interval (GI) combining, in accordance with anembodiment of the invention. Referring to FIG. 3A there is shown acommunication device 300.

The communication device 300 may be similar to the communication devices100A and/or 100B of FIG. 1, and may comprise suitable logic, circuitry,interfaces, and/or code that may be operable to implement variousaspects of the invention. The communication device may comprise, forexample, a host processor 302, a system memory 304, a signal processingmodule 306, a radio frequency (RF) front-end 310, a plurality ofantennas 312 _(A)-312 _(N), and one or more wired connectors 314.

The host processor 302 may comprise suitable logic, circuitry,interfaces, and/or code that may be operable to process data, and/orcontrol and/or manage operations of the communication device 300, and/ortasks and/or applications performed therein. In this regard, the hostprocessor 302 may be operable to configure and/or control operations ofvarious components and/or subsystems of the communication device 300, byutilizing, for example, one or more control signals. The host processor302 may enable execution of applications, programs and/or code, whichmay be stored in the system memory 304, for example.

The system memory 304 may comprise suitable logic, circuitry,interfaces, and/or code that may enable permanent and/or non-permanentstorage, buffering, and/or fetching of data, code and/or otherinformation, which may be used, consumed, and/or processed in thecommunication device 300. In this regard, the system memory 304 maycomprise different memory technologies, including, for example,read-only memory (ROM), random access memory (RAM), Flash memory,solid-state drive (SSD), and/or field-programmable gate array (FPGA).The system memory 304 may store, for example, configuration data, whichmay comprise parameters and/or code, comprising software and/orfirmware.

The signal processing module 306 may comprise suitable logic, circuitry,interfaces, and/or code for enabling processing of signals transmittedand/or received by the communication device 300. The signal processingmodule 306 may be operable to perform such signal processing operationas filtering, amplification, up-convert/down-convert baseband signals,analog-to-digital and/or digital-to-analog conversion,encoding/decoding, encryption/decryption, and/ormodulation/demodulation.

The RF front-end 310 may comprise suitable logic, circuitry, interfaces,and/or code that may be operable to perform RF transmission and/orreception during wireless and/or wired communications, over a pluralityof supported RF bands. The RF front-end subsystem 310 may enable, forexample, performing wireless communications of RF signals via theplurality of antennas 312 _(A)-312 _(N). Each of the plurality ofantennas 312 _(A)-312 _(N) may comprise suitable logic, circuitry,interfaces, and/or code that may enable transmission and/or reception ofRF signals within certain bandwidths and/or based on certain protocols.For example, one or more of the plurality of antennas 312 _(A)-312 _(N)may enable RF transmission and/or reception via the 2.4 GHz, which issuitable for WiMAX, Bluetooth and/or WiFi RF transmissions and/orreceptions. The RF front-end subsystem 310 may enable performing wiredcommunications of RF signals via the plurality of connectors 314. Thewired connectors 314 may comprise suitable logic, circuitry, interfaces,and/or code that may enable transmission and/or reception of RF signalsover wired connections, within certain bandwidths and/or based oncertain protocols (e.g. Ethernet).

In operation, the communication device 300 may be operable performedwired and/or wireless communication, in accordance with one or moreinterfaces and/or protocols supported thereby. In this regard, thecommunication device 300 may be operable to perform transmission and/orreception of RF signals over supported wired and/or wireless interfaces,using the RF front-end 310, and to perform necessary signal processingoperations to facilitate such transmission/reception, using the signalprocessing module 306. The RF signals transmitted and/or received by thecommunication device 300 may carry data pertaining to applicationsrunning in the communication device 300.

In some instances, the RF communication performed by the communicationdevice 300 may incorporate use of the OFDM scheme. Accordingly, invarious embodiments of the invention, the communication device 300 mayconfigured to and/or operable to perform guard interval (GI) combiningduring RF signal reception. For example, OFDM based RF signals may bereceived by the RF front-end 310, wirelessly via one or more of theantennas 312 _(A)-314 _(N) and/or over wired connections via one or moreof the wired connectors 314. The received OFDM RF signals may then besubjected to GI combining, substantially as described with regard toFIGS. 1 and 2, such as during signal processing via the signalprocessing module 306.

FIG. 3B is a block diagram illustrating an exemplary signal processingmodule that support guard interval (GI) combining, in accordance with anembodiment of the invention. Referring to FIG. 3B, there is shown thesignal processing module 306 of FIG. 3A.

The signal processing module 306 may comprise a delay estimator 332, abypass controller 334, a combiner 336, and an extractor 338.

The delay estimator 332 may comprise suitable logic, circuitry,interfaces, and/or code that may be operable to estimate channel delaysduring RF reception operations. The delay estimator 332 may be operableto determine, for example, whether a delay spread associated with aparticular communication channel is smaller than a predetermined maximumchannel delay. In this regard, the predetermined channel delay maycorrespond to, and/or be relevant to guard interval (GI) combining. Inan embodiment of the invention, the delay estimator 332 may comprise afirst multiplexer (MUX) 352 _(A), a second MUX 352 _(B), and a filter354. Each of the first MUX 352 _(A) and the second MUX 352 _(B) maycomprise suitable logic, circuitry, interfaces and/or code that may beoperable to select an output from a plurality of inputs, based on one ormore control signals. The filter 354 may comprise suitable logic,circuitry, interfaces and/or code that may be operable to performfiltering operations, in accordance with specific criteria and/orcontrol parameters, on an input signal. The filter 354 may beimplemented, for example, as a 1-tap infinite impulse response (IIR)filter.

The bypass controller 334 may comprise suitable logic, circuitry,interfaces, and/or code that enable bypassing GI combining in the signalprocessing module 306. In this regard, the bypass controller 334 may beoperable to deactivate, disable, and/or bypass the combiner 336, toensure extracting only OFDM symbols. The deactivation of the GIcombining may be done in certain conditions, such as when thecommunication device 300 is in acquisition mode and/or when thedetermined delay spread of a channel is found to larger than apredetermined maximum delay spread.

The combiner 336 may comprise suitable logic, circuitry, interfaces,and/or code that may be operable to combined extracted portions of theguard intervals with corresponding portions of the OFDM symbols. In thisregard, the combiner 336 may also incorporate additional function toaccount for the combining being performed therein, such as by dividingthe sum by 2 for example. In an embodiment of the invention, thecombiner 336 may comprise a binary adder and a 1-bit shifter.

The extractor 338 may comprise suitable logic, circuitry, interfaces,and/or code that may be operable to adaptively extract portions of theguard intervals. For example, the extractor 338 may be operable toextract ISI-free portions 210 _(B), or part thereof (e.g., part of theISI-free portion 210 _(B) preceding start of shifted FFT windows),substantially as described with respect to FIG. 2.

In operation, the signal processing module 306 may be configured and/oroperable to perform guard interval (GI) combining during signalprocessing of received RF signals. In this regard, the extractor 338 maybe configured and/or operable to extract guard interval (GI) or portionsthereof, during GI combining operations. The extractor 338 may beoperable to, for example, locate the ISI-free portion 210 _(B) of the GI210, and copy that portion for subsequent use in GI combining. Ininstances where the FFT operation applied by the signal processingmodule 306 incorporate a window shift, the extractor 338 may determinethe boundaries of the portion of the guard intervals that is both freeof ISI effects and precedes the start of the FFT window. Combining theGI (or portions thereof) with the OFDM symbol may be performed via thecombiner 336. In this regard, the GI combining may be comprise locatingthe portion of OFDM symbol that corresponds to the extracted GI(portion), then adding the OFDM symbol portion and the GI (portion), andthen dividing the sum by 2 (i.e. averaging).

In an embodiment of the invention, the delay estimator may be configuredand/or operable to perform instantaneous estimate of the maximum delayspread. For example, the first MUX 352 _(A) may select between twoinputs, GI_length, which corresponds to the total length of the guardinterval, and Est_T_(int), which corresponds to an instantaneousestimate of the maximum delay spread, as measured for a particular OFDMsymbol. The filter 354 is then used to filter the output of the firstMUX 352 _(A). In this regard, use of the filter 354 may enable averagingthe per-symbol values obtained from the first MUX 352 _(A) over aplurality of symbols, shown as an average estimate of the maximum delayspread: Est_T_(max). The output of the filter 354, Est_T_(max), iscoupled as an input to the second MUX 352 _(B), with the first input ofthe second MUX 352 _(B) being the GI_length input (same as first MUX 352_(A)). Thus, based on the selection performed by the first MUX 352 _(A),the input of the low-pass filter may be set to either Est_T_(int) (theinstantaneous estimate of the maximum delay spread) or GI_length (thetotal length of the guard interval), while the second MUX 352 _(B) mayenable selecting, as an output, between GI_length and the output of thefilter 354.

The filter 354 may comprise a low-pass filter, and may be implemented asa 1-tap infinite impulse response (IIR) filter having a filtercoefficient α. In this regard, the time constant α of the low-passfilter 354 may be set (equal) to the inverse of the maximum Dopplershift. For example, the output of the filter 354, Est_T_(max) may be setto: T_(max)*(1−α)+T_(int)*α, where T_(max) is the maintained maximummeasured delay value, and T_(int) is the measured instantaneous delayvalue.

Both of first MUX 352 _(A) and second MUX 352 _(B) are controlled usingthe same selection control signal: select_ctrl. The select_ctrl signalmay essentially enable selecting between performing instantaneousestimation of channel delay spread (and thus performing GI combining)and bypassing GI combining. In this regard, when the receiving device(i.e. communication device 300 during reception of signal) may be movingwhile receiving, the delay between the receiving and transmittingdevices may vary, thus possibly causing the instantaneous estimate ofthe maximum delay spread to become inaccurate. Therefore, to avoidinter-symbol interface (ISI) during such transition period, the lengthof GI is used to replace the estimate of the instantaneous delay spread,by asserting/de-asserting the signal select_ctrl, and thus the receivingdevice would use the full length of GI (discard all of it), and the GIcombining function is thus not used for the current symbol.

FIG. 4 is a flow chart that illustrates exemplary steps for adaptiveguard interval (GI) combining, in accordance with an embodiment of theinvention. Referring to FIG. 4, there is shown a flow chart 400comprising a plurality of exemplary steps that may be performed by acommunication device (e.g. device 300 of FIGS. 3A and 3B) to enableperforming adaptive guard interval (GI) combining during communications.

At step 402, a communication device (e.g. device 300) may receive aradio frequency (RF) signal containing one or more symbols preceded bycorresponding guard interval(s). In this regard, the RF signal may bemodulated in accordance with OFDM scheme; with the symbol containingOFDM modulated data and the guard interval (GI) containing a copy of aportion of the OFDM modulated data. In such OFDM schemed, the guardinterval (GI) may comprise a cyclic prefix generated by copying aportion of the OFDM symbol taken at the rear of the OFDM symbol andplacing it (the copy) at the beginning of the symbol, to act as a timebuffer for the transmission of the next symbol so that the currentsymbol does not interfere with the next symbol, due to the effect ofchannel delay for example. In conventional systems, such guard intervalsare considered as overhead, and are simply discarded at the receiverside, and the received RF signal is then frequency down-converted, NDconverted and provided to a baseband processor that then performs timingdetection and delay time estimation. In accordance with the invention,however, guard interval (GI) may be performed during reception of RFsignals.

In this regard, at step 404, the delay time associated with the channelmay be compared with a maximum channel delay. In instances where it maybe determined that the estimated delay time is not smaller than themaximum channel delay, the process may skip to step 410. In instanceswhere it may be determined that the estimated delay time is smaller thanthe maximum channel delay, however, the process may proceed to step 406,where the guard interval (GI) or a portion thereof may be extracted. Inthis regard, the extracted portion may comprise the part of the guardinterval (GI) that is not affected by the inter-symbol interference,corresponding to the difference between the total length of the guardinterval (GI) and an initial portion of the guard interval (GI) that iswithin the estimated delay time. The estimated delay time may beestimated per each received symbol. In this regard, the estimated delaymay be further filtered via a low-pass filter to prevent any falseestimation due to burst noise or the likes. The low-pass filter may beimplemented using a 1-tap IIR filter having a time constant that isequal to the inverse of the maximum Doppler frequency.

At step 408, the receiving device may combine the extracted portion ofthe guard interval (GI) with a corresponding portion of the symbol. Thecombining may comprise a linear addition of the extracted portion andthe corresponding portion of the symbol, with the sum then being dividedby 2 and inserted back to the symbol. The division may be performed as a1-bit right-shift. At step 450, the symbol that contains the combinedportion is then demodulated.

Other embodiments of the invention may provide a non-transitory computerreadable medium and/or storage medium, and/or a non-transitory machinereadable medium and/or storage medium, having stored thereon, a machinecode and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform the steps as described herein for broadbandanalog to digital converter technology.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

1. A method, comprising: receiving by a communication device, a signalcarrying at least one symbol that is preceded by a guard interval thatcomprises a portion of the symbol; extracting a portion of the guardinterval that is free from inter-symbol interference (ISO; and combiningthe extracted portion of the guard interval with the correspondingportion of the symbol.
 2. The method according to claim 1, wherein thereceived signal comprises an orthogonal frequency division multiplexed(OFDM) signal.
 3. The method according to claim 1, wherein the guardinterval is generated based on cyclic prefixing.
 4. The method accordingto claim 1, wherein the combining comprises a linear addition and ashifting operation.
 5. The method according to claim 1, comprisingdetermining prior to the extracting and/or the combining, whether adelay spread associated with the received signal is smaller than apredetermined maximum channel delay for the received signal, and whenthe delay spread is smaller than the predetermined maximum channel delayproceeding with the extracting and/or the combining.
 6. The methodaccording to claim 5, comprising determining the delay spread based on achannel impulse response associated with communication channel used inreceiving the signal, and the channel impulse response is determinedbased on the received signal.
 7. The method according to claim 5,comprising filtering during the determining of the delay spread, aninstantaneous delay spread associated with the received signal.
 8. Themethod according to claim 7, wherein the filtering is performed using alow-pass filter, the low-pass filter comprising a 1-tap infinite impulseresponse (IIR) filter.
 9. The method according to claim 8, wherein thelow-pass filter comprises a time constant that is equal to the inverseof a maximum Doppler frequency.
 10. A system, comprising: one or morecircuits for use in a communication device, the one or more circuitsbeing operable to: receive a signal carrying at least one symbol that ispreceded by a guard interval that comprises at least a portion of thesymbol; extract a portion of the guard interval that is free frominter-symbol interference (ISI); and combine the extracted portion ofthe guard interval with the corresponding portion of the symbol.
 11. Thesystem according to claim 10, wherein the received signal comprises anorthogonal frequency division multiplexed (OFDM) signal.
 12. The systemaccording to claim 10, wherein the guard interval is generated based oncyclic prefixing.
 13. The system according to claim 10, wherein the oneor more circuits are operable to perform the combining via a linearaddition and a shifting operation.
 14. The system according to claim 10,wherein the one or more circuits are operable to determine prior to theextracting and/or the combining, whether a delay spread associated withthe received signal is smaller than a predetermined maximum channeldelay for the received signal, and when the delay spread is smaller thanthe predetermined maximum channel delay, proceeding with the extractingand/or the combining.
 15. The system according to claim 14, wherein theone or more circuits are operable to determine the delay spread based ona channel impulse response associated with communication channel used inreceiving the signal, and the channel impulse response is determinedbased on the received signal.
 16. The system according to claim 14,wherein the one or more circuits are operable to filter during thedetermining of the delay spread, an instantaneous delay spreadassociated with the received signal.
 17. The system according to claim16, wherein the filtering is performed using a low-pass filter, thelow-pass filter comprising a 1-tap infinite impulse response (IIR)filter.
 18. The system according to claim 17, wherein the low-passfilter comprises a time constant that is equal to the inverse of amaximum Doppler frequency.
 19. A system, comprising: a delay estimatorfor use in a communication device, the delay estimator comprising: afirst selector that is operable to select an output from a plurality ofinputs, the plurality of inputs comprising a first input correspondingto full guard interval in a received signal and a second inputcorresponding to an instantaneous estimate of maximum delay spreadassociated with a communication channel used in receiving the signal; afiltering component that is operable to filter output of the firstselector, wherein the filtering performed by the filtering componentsenables averaging values of at least one of the plurality of inputs ofthe first selector; and a second selector that is operable to select anoutput from a plurality of inputs, the plurality of inputs comprising anoutput of the filtering component and the first input of the firstselector.
 20. The system according to claim 19, wherein the filteringcomponent comprises a low-pass filter, the low-pass filter comprising a1-tap infinite impulse response (IIR) filter, and having a time constantthat is equal to the inverse of a maximum Doppler frequency.